Dust flux, Vostok ice core

Two dimensional phase space reconstruction of dust flux from the Vostok core over the period 186-4 ka using the time derivative method. Dust flux on the x-axis, rate of change is on the y-axis. From Gipp (2001).

Wednesday, October 19, 2016

Arctic sea ice still hanging around

Another autumn, another sea ice minimum to add to the chart I have beenpostingyearly for awhile now. This year's minimum was about 4.1 million square km, among the lowest measurements on record.

Nevertheless, there still is not enough information for us to distinguish among several competing hypotheses.

1) The variation in sea ice is part of a dynamic natural cycle, which is currently in a lower area of Lyapunovstability, but which will at some point return to the higher area of stability (as it was prior to about 2003). There are alternatives to this hypothesis, such as the sea-ice system may naturally oscillate between two or more states, but this oscillation is being modified by anthropogenic effects.

If we are observing a natural cycle, and its duration is related to the time observed within the higher area of Lyapunov stability, then at some point the system will return to the area of stability occupied prior to 2003. The typical duration of natural climatic cycles is from a few years to decades. Given the length of time that the system occupied the higher Lyapunov-stable area, I would assume we are looking at a fairly long cycle length--meaning even in the best-case scenario (no anthropogenic effects) we would expect to remain in this state of lower sea-ice extent for at least another decade. A breakout, if it occurs will be towards the right first, before curving up toward the higher area of Lyapunov stability.

If anthropogenic effects are modifying the trajectory of the system, then we may still get an upward breakout, but it may be a short-lived one where the state does not reach the higher area of Lyapunov stability before falling back, either to the current Lyapunov-stable area, or possibly to a new, lower one. Even if, during the breakout, the system reaches the higher area of Lyapunov stability, it may remain there only a short time before returning to the present one or perhaps a lower one.

2) The variation in sea ice extent is in secular decline, likely driven by greenhouse gas emissions, but the dynamics of the natural system have temporarily arrested the decline in the current area of Lyapunov stability. In this case, we may expect the system to remain within this area of Lyapunov stability, before breaking out to the left and arcing downward.

Distinguishing between these differing hypotheses needs more time, but unfortunately we run the risk of an irreversible change occurring as we wait. Better would be to extend the record backwards by several decades, which can probably only be done by collecting near-surface sediment cores, and looking at their microfossils.